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Q: WHY SHOULD YOU USE A CHARGE CONTROLLER TO CHARGE YOUR LEAD ACID POWERPACK BATTERY WITH SOLAR / WIND / PEDAL POWER?   

Short & Easy Answer: Because if you pedal too fast and generate too high of a voltage from your bike generator, you could dramatically shorten the life of your battery / powerpack.

Longer more technical answer:  Your battery / power pack has a limit on how high of a voltage it can see while charging.  One term to describe this voltage is called the "Peak Charge Voltage".  If you pedal too fast and generate too high of a voltage, then you could exceed the peak charge voltage and supply your battery with too much current.  This would damage the cells inside and affect their ability to take a charge. 

 In most cases the peak charge voltage for a lead acid / AGM (absorbed glass mat) battery / powerpack is somewhere near 14.8V DC (V= Volts DC= Direct Current).

This NC25A charge controller has a diversion load output (diversion load slows down or provides a "breaking" function to a wind turbine or over enthusiastic cyclist).  I like hooking the diversion load up to one or two of these 1000-Watt work light stands.   When the charge controller switches into diversion load mode,  the current from the pedal power or wind turbine generator  will be routed into the two 1000 W shop lights.  You may be wondering "How many Watts will actually get dissipated into those two 1000W shop lights?".    We can approximate that by assuming 15 Volts is what is coming off the diversion pin which would cause the lights to glow dimly and dissipate about 200 Watts of power.

Many charge controllers can handle 25 Amps or more, but there aren't many that can handle a very high input voltage.  This is because most charge controllers use FET transistors to do pulse width modulation.  The lower cost FETs can only usually handle 35 to 45V max input voltage.   The  NC25A charge controller uses a mechanical relay to switch the voltage on and off to the lead acid battery and has a max input voltage of 130 Volts.    After searching the internet I have found that there is no other controller selling for this price that can handle that kind of high input voltage.    

I took a look at a 35 Amp charge controller made by Sunforce and it can handle a max input voltage of 35 Volts.  That kind of controller could easily get blown if you are using it and when the battery gets fully charged, the controller opens up the connection to the battery, and then your pedal power generator voltage shoots up to 40 Volts DC.  Then suddenly your Sunforce is permanently damaged.  Also the Sunforce does not have the ability to use a diversion load which would act as a braking system to slow your pedaling down. 

Below shows a graph of battery charge voltage.  This data is just for the geeks.  It's not necessary to understand what this is to charge your batteries.

Below, you can see a LabVIEW WattsVIEW test software graph where this FexchargeTM NC25A charge controller was tested on a pedal power bicycle generator providing power to a television under these conditions:

• Pedal Power Bike Generator was being driven at a constant velocity of 15 miles per hour
• The NC25A 12V charge controller  max charge voltage was set to 14.8 volts DC which is the appropriate level to charge a lead acid AGM (Absorbed glass mat) spill proof battery.  This is what you will find in 95% of portable powerpacks.
• The pedal power bike generator was hooked up to a Duracell 600W power pack that had a state of charge of 90%
• While this experiment was going on, the Duracell Power pack was delivering power to a 110 Volt AC Toshiba 60 Watt color television.
• You can see by looking at the blue trend line on the graph below that the total output power being produced by the pedal power bike generator was about 140 Watts.

Below you'll see two WattsVIEW graphs which are both showing 5 minutes of data.  The white line on the left chart below represents measured voltage at the battery / powerpack.   The red line below on the left graph represents current or Amps.  The blue line on the graph on the right shows you power or Watts.   Every time the NC25 Charge controller detects that the battery voltage is getting too high,  you can see the trend representing Amps and Watts go down to zero.

Below you can see where the charge controller determines that the battery has reached the specified charge voltage threshold, it breaks the connection between the pedal power bike generator and the battery / Powerpack.   The red plot line below drops from 9 Amps down to 0 Amps.  When this happens, current stops flowing from the pedal generator into the battery and the battery voltage shown as the white trend line below begins to droop down from 14.8V down to 14.2.  When this happens, the NC25A charge controller turns back on and once again starts to let current flow from the bike generator to the battery.  

Once this 12V DC charge controller opens up its contacts and disconnects your bike generator from the battery power pack being charged,  it will divert your energy to another path.  You can choose to let it divert to a 2nd NC25A charge controller to charge another lead acid battery powerpack, or just a dummy load like to the heating element of a hot water heater, or a pair of 500 Watt outdoor flood lights, or a fan, or whatever you choose.  For more information see the owner's manual.  The diversion load is only needed if you are a hard core work out athlete who always wants to feel some kind of resistance pulling your bike trainer.  

NOTE:  This charge controller will not serve as a regulator since it  has a slow response time and would have too much over shoot and under shoot to maintain a constant voltage.  I had my hopes up that it would do that , but it does not. 

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